Osteogenesis imperfecta (OI) is a rare hereditary bone fragility disorder that affects 6-7 per 100,000 populations, and pituitary stalk interruption syndrome (PSIS) is a rare congenital defect with varying degrees of pituitary hormone deficiency, affecting approximately 0.5 in every 100,000 births. Currently, only two cases of these complications have been reported. A 46-year-old male who had experienced more than 20 fractures (peripheral and vertebral) during adolescence visited our hospital for close examination. He presented with blue sclerae and long bone deformations. We suspected OI because his mother and sister, who were being treated for osteoporosis, also had blue sclerae. Genetic testing identified a heterozygous variant (c.757C > T, p.Arg253Ter) in the COL1A1 gene, leading to the diagnosis of OI. His mother and sister also had the same variant. Considering that he underwent GH replacement therapy for his short stature during his childhood, his pituitary hormone levels were also evaluated to know if GH deficiency impacted low bone density; hypopituitarism was then suspected. The pituitary function test results led to the diagnoses of hypothalamic GH deficiency, hypogonadism, hypothyroidism, and hypoadrenocorticism. Furthermore, magnetic resonance imaging showed anterior pituitary atrophy, pituitary stalk loss, and ectopic posterior pituitary, leading to the diagnosis of PSIS. The combination of OI and hypopituitarism may have caused further bone fragility. Therefore, although rare, clinicians should keep in mind that patients with OI can possibly have concomitant pituitary insufficiency, which can lead to developmental and growth retardation.